


SOULs are a powerful thing

by zerocity



Category: Undertale (Video Game)
Genre: Child Abuse, M/M, Medical Experimentation, Other, Rape, Soul Sex, gaster is a bad dadster, noncon, soul experimentation
Language: English
Status: Completed
Published: 2016-09-08
Updated: 2016-09-08
Packaged: 2018-08-13 20:08:38
Rating: Mature
Warnings: Rape/Non-Con, Underage
Chapters: 1
Words: 3,304
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7984537
Author URL: https://archiveofourown.org/users/zerocity/pseuds/zerocity
Summary: <blockquote class="userstuff">
              <p>Gaster experiments on a SOUL for the good of the Underground.</p>
            </blockquote>





	SOULs are a powerful thing

**Author's Note:**

> I wrote this based off a couple of [Askellie's](http://askellie.tumblr.com) prompts they put up for adoption.

Gaster had been very busy lately trying to solve the Underground’s number one problem, dumped onto him by King Asgore himself: Finding a power supply to fulfill the needs of the underground. It felt like the answer was right in front of him but he couldn’t see it, no matter how hard he looked.

Eventually he came up with an idea: Magic. Magic is a very powerful substance and abundant through the underground, and if they could just harness that energy, maybe they could power their homes and businesses with it.

Harnessing that energy was the problem though. Magic existed inside of monsters and thus was unaccessible to get his hands on. The magical bullets that monsters formed was a more diluted, concentrated emotional power of magic that held very little actual energy, but maybe if he could get some of the source of the magic, he could test to see whether his idea had grounds to stand on or not.

Unfortunately, doing this kind of testing was deemed… immoral by the King and of course, the rest of the Underground’s population.

But what they didn’t know didn’t hurt them, and if it ended up being as powerful as Gaster’s theories sound, it would be an extremely potent energy source. All he needed was a sample to begin.

-

Gaster was sitting at home in the dark with only his computer monitor to light the room. He was disturbed by a knocking sound at his door, and with an exasperated huff he answered.

“Come in.”

The door creaked open slowly, revealing a pale white faces poking out from behind the door.

 

“dad, can you help us with our homework?”

Gaster planted his elbows on the table, palms of his hands on his forehead as if nursing a headache.

“Not tonight. I’m very busy, boys.”

“oh... okay,” Sans said disappointedly. He turned to leave and shut the door behind him, but Gaster quickly got an idea.

“Wait, Sans. Come here.” 

After a pause, Sans pushed the door back open and came to stand in front of Gaster.

“How would you like to help Daddy with his research?”

Sans eyes lit up at that. Gaster knew he liked science, remembering all the times he found the boy rifling through his theories and papers and finding things scattered about when he hadn’t been home for a couple of days.

“what do you need help with?” Sans asked curiously, looking up at him with bright white eyes.

“Well, I need to run a couple of tests for a project I’m working on, but I don’t have any volunteers. It would really help me if you joined me at the Lab tomorrow.”

“really?”

“Yeah, I think you could be a big help to me. What do you say?”

“yeah! that sounds cool.” The small skeleton giggled and hugged him as best he could while Gaster was still sitting.

“Alright then, off you go. I’ve got to finish up these papers, I don’t want to be bothered for the rest of the night now so go on.” He shooed Sans away and turned back to his computer to look over his notes again.

“thanks dad!”

God, what was he thinking? But if this worked out, most of the Underground’s problems right now would be solved.

He could only hope that it would be so simple.

\--

The Lab was the most technologically impressive place in the entire Underground, but with the oncoming power crisis and frequent blackouts, they were running out of time.

Gaster held Sans wrist fast as they walked quickly through the sparsely populated Lab, Sans held onto Papyrus’ arm and dragging him behind as they tried to keep up with Gaster’s pace. They approached the elevator that led to the top of the Lab, where Gaster’s office resided. Upon reaching the top, the children poured out of the elevator and rushed to the office door, slamming themselves on the wall and giggling to themselves. 

Gaster simply approached the office and entered his keycard, the door swished open and he stepped foot inside.

“Sans, come in.”

Sans walked to Gaster’s side and Papyrus followed right behind him.

“Ah-ah, Papyrus. You can’t come in here,” Gaster grabbed Papyrus wrist and left the room, darting down the hall and around the corner, setting him down on a bench. “Stay here until we are done. Don’t move from this spot, it won’t be that long. We’ll be back soon.”

“OKAY…” He stood and left Papyrus there, hoping he would stay put. There were some magazines nearby, maybe those would keep him entertained.

“Let’s just get started,” Gaster shut the door behind him and walked over to the counter, putting white gloves on and picking up a clipboard. Without turning around he commanded Sans.

“Take your shirt and coat off and get on the table.”

As Sans did as he was told, Gaster walked to the corner of the room and wheeled over a small machine, pushing it next to the examining table. The machine was decorated with several measuring equipment and complex wires.

“Okay Sans, I need you to summon your SOUL.”

“my soul?”

“Yes, the tests we are doing today are about your SOUL. You remember how to summon it, correct?”

“uh, yeah.”

Sans closed his eyes in quiet concentration and held his hands close to his ribs. Quickly a faded grey heart manifested, glowing faintly inside of his chest.

“Good. Now lay down, I am going to take your SOUL and attach it to this machine to gauge its electrical output, well, if there was any.”

After some hesitation, Sans complied and laid on his back, shutting his eyes and holding his breath as Gaster reached inside of his chest and grabbed the small grey heart gently. He brought it out and set it on the small surface of the machine. He looked down at the clipboard, double checking his work before he was interrupted.

“dad?”

There was another beat of silence before Gaster set the clipboard down and got to work. He held his hand around the SOUL as if to catch it if it dropped and grabbed a small needle wired to the machine with the other, about the width of a nail.

“Sans, this may pinch, and it might feel cold so brace yourself.”

He gave him a moment to prepare before slowly pushing the needle inside, the metal passing through the protective magical barrier with a bit of pressure. Gaster heard Sans made a noise to the side and the sound of paper ripping but he stayed fully concentrated on the SOUL.

When it became obvious the needle wouldn’t slip from its position as soon as he looked away, Gaster looked down and read some of the measuring dials. The readings were normal for monsters Sans’ age, and there was some slight electrical activity but of course there was, the SOUL held a lot of power but the real question here was how to harness it.

You couldn’t use monsters themselves as an energy source, the King would never hear the end of it if that was what the conclusion of this experiment came to. There had to be some other solution that he wasn’t seeing.

Snapping himself from his thoughts, Gaster craned his head to look at Sans. His eyes were closed tight and he was gripping the table below him.

Curious, he had to ask.

“Sans, how do you feel?”

Sans only shook his head weakly in response to the question.

 

“Right, okay let’s get this out of you,” carefully he took hold of the needle and slipped it out of the heart. Sans gasped in a breath as if he had been underwater for ten minutes. Gaster checked the SOUL for any damage, there was a noticeable indent where the needle had been, but that would easily heal.

Sighing, he sat the needle down and gathered the clipboard again to review his notes. The only other options he had were to dissect the SOUL, which wasn’t really possible with how frail Sans was and how weak monsters in general were, besides if the King found him dissecting and experimenting on monsters he would be fired in a heartbeat.

Option B was to get a sample of pure magic from the SOUL and test that, though getting it through that method proved… questionable.

Monsters only allowed their SOULs to appear before a doctor in order to get healed if they were sick, or if they were very intimate with a lover, though most monsters still never showed their SOUL in such a vulnerable way, and beyond that, a raw display of magic was rare and required stimulation, to put it lightly.

Gaster didn’t want to touch Sans that way. This was about science. This was purely for medical and scientific reasons. Maybe he could trigger the reaction a different way? Maybe he didn’t have to do it this way at all.

But right now he had a subject right in front of him. It would be easier to use Sans right now than work with someone else who may not approve of his methods or blab to the King about this. Besides, Gaster was Sans’ father. He could make sure the child never told anybody about this and explain it to him in a way that he would understand.

He walked over to the examination table and hovered over Sans, who was looking up at him now with wide eye sockets.

“Sans, I have another test I need you to help me with,” Gaster reached for Sans’ arm, holding it firm and tying straps from the side of the table tight through his radius and ulna bones.

“ah, what are you doing?” Sans pulled against the restraints with his spare hand. Gaster leaned over him further, gripping his free wrist and pinning it to the other side before tying it down too.

“Sans I need you to cooperate with me. This is very important.”

“why are you doing this?”

“Just be patient and this will be over soon, faster if you just stay still.”

The boy became quiet and stopped moving too. Now Gaster could finally concentrate. He turned to face the machine and picked up the SOUL.

Right now the only thing he wanted to get this over as quickly as possible and without incident.

“I’m going to touch your SOUL and you are going to tell me truthfully how you feel.”

Sans nodded in response.

Gaster gave the SOUL a testing touch through gloved hands, though he couldn’t feel anything interesting or special about it, which was a good thing. The gloves were protecting him from Sans’ emotions. If at all possible he would like to get through this without being invaded by Sans’ feelings.

Though these SOULs were very interesting. He would love to fully experiment with them if it weren’t explicitly forbidden by, well, everyone and included in the Royal Oath he swore in front of the King when he took this job. There were some interesting theories about them that would never be put to use because it was ‘not right’ or ‘immoral.’

What a shame.

Lost in thought he found himself rubbing circles into Sans’ soul with his thumb. He looked over at the small skeleton, he looked like he was trying to stay as still and quiet as he could, but shook slightly and small pants left his mouth.

“How does this feel?”

“...weird.”

 

“Weird how? Can you describe it?”

“n-no, just stop, please.”

 

“Does it feel good at all?”

A pitiful whine escaped his mouth and he writhed on the table.

“Alright,” he stopped his prodding and set the heart back down on the machine’s surface where it hovered gently above, “but this will only get easier if you are honest.”

This wasn’t working. How could he stimulate his SOUL enough to cause release without actually touching it?

Maybe he could try electrocution? That caused stimulation in the muscles, maybe it would work for the SOUL as well? Although it might cause Sans discomfort, the results are the only thing that really mattered at this point.

He reached for a cabinet and pulled out a small, rounded silver device, raising it up so Sans could see it.

“what is that?”

“This will administer an electric shock. It will be light, and hopefully not painful but do tell me how you feel.”

Gaster flipped the switch on the side, causing the device to stir with power and pressed it to the SOUL’s surface very lightly.

Sans curled up on himself and his bones rattled together. Gaster removed the device.

“How did that feel?”

Sans shook his head rapidly.

 

“d-don’t! please don’t do that again. please...”

“How did it feel though? Describe it to me.”

He shook his head again.

“Are you sure this isn’t working? It didn’t feel good at all? Let’s try again.”

Gaster applied the device back to the surface of Sans’ soul. Instantly Sans reacted, body locking up against the restraints and breath hissing between his teeth.

“stop, please...” His voice cracked as he spoke.

“Ugh. Very well.”

As much as he didn’t want to admit it, there was no way to make such raw magic come from his SOUL like this. This was getting worse the more things he tried and as much as he hated it, he would have to do this manually. He set the device down and removed his gloves.

“I thought we could do it differently but apparently not, but this might feel better for you now. Just try to relax.”

Gaster picked the light grey heart up gently and started to rubbing gentle circles into it just as before. This time instead of strangled gasps coming from San’s mouth, there was hushed panting quickly getting louder with every push and pull of his SOUL.

Now emotions from Sans’ SOUL was invading him, this mix of nervousness and pain surrounded by an overwhelming feeling was hitting him harder and harder every second he touched it and it was becoming harder to think clearly. He had to stay determined though, do this for the results. Do this for science, don’t lose yourself.

He snapped to when he heard the distracting noise of Sans’ moans filling the room.

“Be quiet.”

Sans became a little less noisy but still, the sounds that he made were the only ones filling the room. Stay focused Gaster. Just focus on getting the magic and that’s it. That’s what he was here for.

Gaster let his body slump against the wall as he continued rubbing the magical core. God, he couldn’t deny that it felt good to do this again. It was such a long time since he’d done this, even with his own SOUL. And this one was so pure and untainted and soft and beautiful.

The SOUL began to build pressure and Gaster could feel it in every bone in his body, too overpowering for him to think. He pressed harder and harder into the SOUL until finally the pressure broke, releasing mind numbing pleasure over his entire body faster than he thought it would. The light grey thing in his hands burst with pure white liquid, flowing over his hands and spilling onto his lab coat.

He shuddered and let himself fall to the ground. Once the static in his head dissipated, he stood to his feet shakily.

Yes! He did it. He got the raw magic sample he needed but quickly the reality of the situation was settling in.

What the fuck did he just do?

He turned around to see Sans lying on the examination table still, breathlessly panting and curled in on himself as much as he could manage while his arms were still held fast by the restraints.

Gaster would have to deal with him in a moment. Right now he needed to analyze the magical sample. He shakily walked over to the machine and wiped as much of the magical fluid onto the surface. Pulling out the device and sticking it in the magic, the gauge that detected electricity from the magic.

It was positive!

...But it was barely anything. No where near enough to power anything of any importance. It might as well have been nothing at all for what it was worth.

Anger would have been an understatement for what Gaster felt. This entire experiment was completely worthless.

“You are so useless Sans,” he spat those words venomously and shook with the post-climax high that he’d felt from Sans’ pathetic little soul, “You were always useless.”

Sniffling came from the other side of the room. Sans had his head turned as much as he could from Gaster and was crying into the table.

Fuck. Control yourself. He couldn’t let his emotions get the better of him now, the King know what he’d done, he couldn’t let anyone know and now he would have to make sure Sans never told anybody about this. Everything was still under control.

Gaster walked over to him and started to untie him.

“Get up,” He pulled Sans by the arm roughly off the table, handing him his clothes and exchanging himself a spare clean lab coat as well, “put these on and let’s go home.”

He pulled the child out of the room easily and walked quickly down the hall to find Papyrus, who was where he’d left him but laying on the floor reading magazines.

“Papyrus, come,” he called.

 

“OKAY DAD!” The small skeleton hopped up and came to Sans’ side, holding onto him as he was pulled limply through the hall to the elevator.

“HOW WAS THE TEST SANS?”

Sans said nothing, instead Gaster could feel him looking up at him, as if he would give him the answer. He only gripped Sans’ wrist tightly and sighed, not looking at either of the children.

“WHAT’S WRONG?”

 

“it’s fine, pap. i’m just tired is all,” his voice was hollow as he spoke.

Well, at least he was a fast learner.

“Be quiet, both of you. I don’t want to hear another word until we’re back home.”

Sure enough, the two children didn’t say a peep until they reached their home in the Capital. Once they entered their house, Gaster made a B-line down the hall and to his room, dragging Sans along behind him.

“I need to have a word with your brother, Papyrus. Stay there.”

Gaster bust through the door to his room and closed it behind him, pulling in after him.

“You won’t tell anybody about that Sans. Not your brother, not anybody. If I find out you’ve told anybody you will be punished, do I make myself clear?” He spoke in an angry hushed voice.

Sans tried to hide his face with his sleeve as tears formed at the corners of his eye sockets and he tried to pull away from Gaster.

“Answer me,” Gaster gripped his arm tighter. Sans stilled in his grasp.

“i won’t tell anyone, i won’t ever tell anyone. i promise. let me go.”

“Good. Now get out.”

Sans closed the door quietly behind him, leaving him alone.

Gaster sat down in his chair and took a bottle of aspirin from the desk drawer, taking two down before he rested his elbows on the desk and covered his face with his hands.

He sat in the dark like that for a while just thinking.

It was for science. It was a one time thing and he learned a lot from it. There was nothing actually wrong with what he’d done and no one would ever know anyway and it would never happen again so it’s not like it mattered. Anybody in his position would have done the same thing too, especially with the kind of pressure he was put under.

Everything would be fine.

**Author's Note:**

> My tumblr is [zerocity.tumblr.com ](http://zerocity.tumblr.com)


End file.
